1. Field of the Invention
The present invention relates in general to base transceiver stations of digital mobile telecommunication systems, and more particularly to a base transceiver station of a digital mobile telecommunication system wherein a radio frequency (RF) unit is separated from the base transceiver station and installed remotely therefrom and a remote interfacing unit is installed between the base transceiver station and the RF unit to remotely control and monitor the status of the RF unit via an RF cable.
2. Description of the Prior Art
Generally, a base transceiver station of a digital mobile telecommunication system functions to transmit and receive data and voice over a radio channel, control a terminal (e.g., a personal communication system (PCS) or digital cellular system (DCS) terminal), monitor the quality of speech of the terminal and interconnect the terminal and a base station controller (referred to hereinafter as BSC). Namely, the base transceiver station is located between a mobile station and a BSC to interface between wired and wireless channels and perform main functions associated with a radio link. For example, the main functions associated with the radio link may be a function of allocating and managing forward link power to code division multiplex access (CDMA) frequency, channel and frame option resources, a function of processing an outgoing call signal, incoming call signal, soft handoff call signal and hard handoff call signal and a function of receiving and managing global positioning system (GPS) timing information and providing system timing information to the mobile station and base transceiver station.
The base transceiver station is further adapted to perform a function of transmitting and receiving radio signals over a pilot channel, synchronization channel, access channel, paging channel and traffic channel, a function of routing traffic and control information to the BSC and error detection/statistical information collection/report functions.
With reference to FIG. 1, there is shown in block form the construction of a conventional base transceiver station of a digital mobile telecommunication system, which is denoted by the reference numeral 20. As shown in this drawing, the base transceiver station 20 comprises a base transceiver station control processor (referred to hereinafter as BCP) 21 for managing and controlling the entire operation of the base transceiver station 20, a base transceiver station interconnection network (referred to hereinafter as BIN) 22 for performing a packet router function between the base transceiver station 20 and a BSC 10 through an E1 line or T1 line and interfacing high-level data link control (HDLC) packet data between processors in the base transceiver station 20, and a time and frequency unit (referred to hereinafter as TFU) 23 for generating a reference frequency and timing synchronization signal to synchronize the processors in the base transceiver station 20 and perform timing synchronization with an adjacent base transceiver station. The base transceiver station 20 further comprises a digital unit (referred to hereinafter as DU) 24 for modulating and demodulating data and voice signals being transmitted and received over a CDMA channel, and an RF unit (referred to hereinafter as RFU) 25 for converting an ultrahigh frequency (UHF) signal from a mobile station into an intermediate frequency (IF) signal, transferring the converted IF signal to the DU 24, converting an IF signal from the DU 24 into a UHF signal, amplifying the converted UHF signal to a predetermined level and radiating the amplified UHF signal over the air.
A description will hereinafter be given of detailed functions of the above-mentioned components of the conventional base transceiver station 20 of the digital mobile telecommunication system.
The BIN 22 provides an interface with the BSC 10 and an internal communication line to the base transceiver station 20 on the basis of the packet routing function.
The BCP 21 controls and diagnoses the entire operation of the base transceiver station 20 and performs an appropriate operation based on the diagnosed result. Further, the BCP 21 acts to download software associated with initialization of the base transceiver station 20.
The DU 24 acts to process voice and data signals being received and transmitted from/to each terminal. In particular, the DU 24 is adapted to process all signals associated with CDMA.
The RFU 25 functions to convert modulated data and voice signals from the DU 24 into RF signals, transmit the converted RF signals to a terminal, demodulate modulated data and voice signals from the terminal, convert the demodulated signals into digital signals and transfer the converted digital signals to the DU 24. The TFU 23 functions to receive information relating to a reference time necessary to the base transceiver station 20 from a GPS and supply the received information to the base transceiver station 20. As a result, all units in the base transceiver station 20 are synchronized with a GPS time and thus have the same timing.
However, the above-mentioned conventional base transceiver station of the digital mobile telecommunication system is disadvantageous in that all components are installed therein, resulting in an increase in the volume of the base transceiver station. Further, a loss on a path to an antenna of the base transceiver station is increased and thus becomes a problem in designing transmission/reception stages. In particular, a small-sized base transceiver station or micro-sized base transceiver station may employ a high power amplifier (HPA) installed in its main hull, leading to an increase in the volume of the base transceiver station. This swims against a recent trend where the base transceiver station gradually becomes smaller in size and lighter in weight.
Furthermore, the use of a number of frequency allocation (FA) frequencies requires a larger number of HPAs in consideration of the capacity of the base transceiver station. Provided that the base transceiver station accommodates all of such HPAs, it will become much larger in volume. This larger volume of the base transceiver station results in a limitation in regard to the place of installation. As a result, the base transceiver station cannot be installed in a place effecting the optimum propagation and thus improve the quality of speech.
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a base transceiver station of a digital mobile telecommunication system wherein a radio frequency unit is separated from the base transceiver station and installed remotely therefrom and a remote interfacing unit is installed between the base transceiver station and the radio frequency unit to remotely control and monitor the status of the radio frequency unit via a radio frequency cable, thereby making the base transceiver station smaller in size and lighter in weight.
In accordance with the present invention, the above and other objects can be accomplished by a provision of a base transceiver station of a digital mobile telecommunication system comprising a master base transceiver station device (master BTS device) and a plurality of remote radio frequency units separated from the master BTS device and installed at a remote site therefrom for processing radio frequency signals, wherein the base transceiver station further comprises remote interfacing means installed between the master BTS device and the remote radio frequency units for a) transmitting control commands to the remote radio frequency units in response to control data from the master BTS device to monitor and control the status of the radio frequency units; b) supplying and monitoring operating power to the remote radio frequency units; and c) receiving status values from the remote radio frequency units and interfacing them to the master BTS device.
Preferably, the remote interfacing means may include a central processing unit; a transmission modem for modulating the control data from the master BTS device in a frequency shift keying manner and transmitting the modulated control data to the radio frequency units; a frequency divider for dividing the frequency of output data from the transmission modem into different frequencies; a plurality of diplexers, each of the diplexers transmitting a corresponding one of output signals from the frequency-divider to one of the radio frequency units associated with a given sector at a transmission frequency and receiving the status value from the corresponding radio frequency unit at a reception frequency; a plurality of reception modems for demodulating output data from the diplexers in the frequency shift keying manner, respectively; and a signaling connection controller for receiving output data from the reception modems and sending the received data to the master BTS device.
More preferably, the master BTS device and the remote interfacing means may perform communication with each other according to an RS-232 communication protocol and an RS-422 electrical interface standard, and the remote interfacing means may transmit the control commands to the remote radio frequency units and receive the status values therefrom via radio frequency modems. Further, the remote interfacing means and the remote radio frequency units may be interconnected via a coaxial cable.